Art of removing metals as volatile chlorides from ores and other matters containing the same



Patented Feb. 18, 1936 UNITED STATES ART OF REMOVING METALS as vonA'nLE CHLORIDES FROM ORES AND 'o'rnna MATTERS CONTAINING THE" SAME .Charles'Hai-t, Chester, ia, assignor of one-half g to Peter Shields, Washington, I). 0.

No Drawing. Application April 21, 1934,

Serial No. 721,827

.1 Claims. (01. 75-67) This invention relates to improvements in the removal and segregation of metal values from ores and other matters, by selective heating and chlorinating operations.

In my prior Patent No. 1,826,932 and its Reissue 18,609, is described a procedure of expelling a portion of the iron content from a complex ore; and my copending application Ser. No. 711,280,-

filed February 14, 1934, discloses the selective expulsion of iron and nickel and/or cobalt.- The present invention goes beyond these disclosures,

and provides a means of obtaining a concentration of essentially all the metal values, as 'distinguished from gangue, of a-complex material (including ores) which contains the same, and of segregating these values. This is attained by selective chlorinating and heat treatment, where'- by nickel and also the highervolatilizing chlorides of metals are expelled. As a particular in-r stance, it is thus possible to recover the chromium values from complex matters, where the large quantities of other metals and gangue render such matters uneconomic for commercial treatment with prior processes; and where the value of the other metals cannot be exploited because of the presence of the chromium and the gangue. It will be understood that by gangue, I refer to the presence of concomitant materials of low normal value, such as the silica and alumina (as such or as complex silicates and aluminates binding metal values) of ores. Furthermore, the percentages of valuable metals differ in various specimens and it is desirable, as brought out in the uct, in cases where a blending thereof is to be produced for attaining alloys and the like thereof.

Accordingly, it is a feature of the present in-' vention that such matters are subjected to selective heat and chlorinating treatment whereby. the metal values are recovered in concentrated or enriched form, while major portions of the gangue matter are eliminated from the collected metal' blending in the desired proportions for preparing alloysand the like thereof. These chlorides may also be converted to the oxides or other salts prior to blending; or selective condensation may be so conducted that several chambers at successive 5 temperature decrements receive precipitated mixtures in the desired proportions thereof.

The process may likewise be employed as an I adjunct to procedures disclosed in the copending application, as a means of recovering further 10 metal values, including chromium, occurring in the residue therefrom.

The following examples are given as illustrative of a large range of treatments, all terminating in the driving off of substantially all metal values.

' "Ezramplel A Cubanlaterite ore, of the general analysis set out in my said patent, and as occurring in the Mae and Mayarl beds, for example, is subjected after 20 thorough drying, to a low temperature sponging (at around 1000 degrees C., i. e. substantially without any sintering, in order to maintain a maximum surface for reaction) in the presence of a restricted quantity of carbon, so that a portion at of the iron content thereof is reduced to elemental iron, and likewise a portion of the nickel content (usually present as garnierite) is reducedto elemental form. It has been found with such sponging that by selective control of the time temperature and amount of carbon, say 64 percent of the iron and 91 percent of the nickel may be reduced: while by a farther-going sponging, 83 to percent of the iron and around percent of the nickel may be reduced. The chromium and iron 85.

present in chromite remain substantially unaffected along with a portion of the iron which appears to be present as oxide but is not reduced under the conditions stated. The sponge contains, by preference, less than 1 percent of carbon. 40 The sponge, while still hot and hence free from combined water or water vapor, is brought into contact with chlorine, which may be at a pressure slightly above atmospheric. The temperature is maintained between 400 and 900 degrees C., and is regulated according to the time of treatment and the conditions of condensation. At 500 degrees 0., from 85to 95 percent of the elemental iron in the sponge is driven off in the form of ferric chloride, which forms and sublimes readily at 50 such temperature; while only a small proportion of the elemental nickel passes ofi, although an extensive chlorination, thereof appears to occur. The unreduced oxides in the sponge are but little affected at temperatures up to 700 degrees. Iron 55 in the form of oxide is only driven off to the extent of about G-percent of its total quantity at 700 degrees, owing to the substantial absence of a. reducing agent; while nickel oxide shows a slight gain in weight probably due to a metathesis to-nickel chloride, but little escape of this nickel chloride occurs below 700 degrees under such conditions.

-. At 800 degrees, about 80 to '90 percent of the elemental nickel has been chlorinated and driven off. In general, it may be stated that elemental iron, nickel and cobalt show definite indications of chlorination below the boiling points of the chlorides, and even below the temperatures of active evolution or sublimation of these chlorides.

The control of the'heat, of the chlorine admission, and of the time of treatment, therefore, enables the operator to drive off from the pre-reduced ore or sponge pre-determinable quantities of iron and nickel, in the form of chlorides, while the remaining iron and nickel constitute a part of a general residue also containing the chromium value and gangue. By restricting'the quantity of carbon left in the sponge, it is found that the temperatures employed lead to substantially no chlorination of the silica and alumina occurring in the gangue, although an apparent change ormodification occurs in the ore which permits a magnetic or gravity separation of an enriched portion, if desired, which contains iron, nickel and chromium. The heating and chlorinating operation is not apparently attended by the formation of any carbonyls, possibly by reason of the relatively low temperatures at which such compounds are decomposed, and the substantial absence of water vapor .and excess carbon. The absence of water vapor also appears to prevent the formation and retention of any great quantities of iron as ferrous chloride. The evolved vapors may be handled as in my aforesaid application.

The chromium content is substantially unaffected in the sponging operation, and practically no chromium values evolve as chlorides at temperatures below 700 degreesC. Above 700 degrees a certain amount of chlorination proceeds, especially if carbon is present. At 800 degrees,

.about 95 percent, and at 900 degrees about 80 percent of the original chromium remain in the residue: the evolved chromium chloride at such temperatures may be separated by fractional condensation ahead of the nickel chloride.

It is therefore preferred to conduct the heating and chlorination of the spongein two phases: ((1) approximately 500 degrees C., at which an active evolution of ferric chloride occurs substantially free from nickel chloride (12) approximately 800 degrees C., at which the nickel chloride is driven oif with most of the remaining ferric chloride (a few percent of the total original iron). The ferric chloride from the first phase may be burnt imwith a further quantity of fine carbon and again,

subjected to the action of chlorine at high temperature; or is smelted to reduce the chromite, and then treated with chlorine at high temperature. As the temperature rises, the iron and other metal oxides and salts are broken down. The presence of the chlorine in the same or a subsequent treatment, therefore, causes the evolution of the iron, nickel, and chromium chlorides at the successively increasing temperatures: the iron coming over at below 500 degrees; the nickel at 700 to 800 degrees, and lastly the chromium. Where chromite .is present, with carbon, this breaks down at above 900 degrees, and immediately chlorinates as simple chlorides, and begins to pass over. It is preferred, however, to carry the temperature above 1000 degrees; and it is best to carry the temperature at least to 1100 degrees, to obtain a clear expulsion of the metal values. As a result thereof, over 99 percent of eachof the values of iron, nickel, and chromium contained in the original ore,-are driven off.

During this secondary chlorination, certain quantities of the silica and alumina are likewise attacked; but it is characteristic that the quantities may be controlled by regulating the time, temperature, amount of carbon, and the rate of chlorine introduction. 'An economic compromise can thus be effected on the basis of chlorine losses in cycling,

The issuing vapors are led through a fractional condensation duct, and the chromium and nickel chlorides permitted to deposit, which they do at their selective temperatures, with a substantial segregation. The more highly volatile iron, silicon, and aluminum chlorides pass on through, and a further cooling may then be employed to throw down the ferric chloride. The silicon and aluminum chlorides, however, represent a loss of the valuable chlorine; and hence they are preferably contacted immediately with hot air or oxygen, so that the oxides are formed, and the chicrine is ready for cycling again. Even the iron chloride may be left in the vapors, and the iron, silicon, and aluminum oxides formed by the burning; with the chlorine for cycling. The precipitated oxides are valuable in many arts, owing to their fineness of texture.

It will be noted that the ratio of nickel to chromium can be regulated in several ways. Where the temperatures of initial treatment of the sponge are low (circa 800 degrees), little chromium is evolved; and if the treatment is continued a sufllcient time at such a temperature, a major part of the nickel is driven off, while the residue contains most of the original chromium, which is evolved in the secondary treatment. On the other hand, if the time of such chlorine treatment is shorter, less nickel is evolved, and more passes to the secondary treatment. ther, the manner of conducting the sponging itself may be employed in determining the-ratios; as pointed out relative to the selective reduction of iron and nickel oxides therein.

Example II A similar treatment may be conducted, but at the expense of time and cost of heatin g,'by carrying the chlorination of the original sponge to a temperature above 900 degrees, so that a decomposition of the chromite occurs in the substantial absence of a reducing agent; and the chromium and iron are directly expelled as chlorides.

Example III Where a quick elimination of the metals is desired, without niceties of segregation, and where chlorine losses may be cheaply made up or aluminum chloride provides a by-product outlet, the ore or other matter may be calcined to expel Fur- I moisture, mixed with carbon, and subjected to chlorination at increasing temperatures. The concurrent presence of carbon and chlorine leads to the formation and evolution of ferric chloride at such a rate that most of the iron is expelled before the temperature reaches 500 degrees, and the ferric chloride may be separated and exploited as such as set out above, or sold as recovered. From 500 to 7.00 degrees C., the major portion of the vapor is nickel chloride. Up to 900 degrees C., very little silicon or aluminum cor;

ponent is converted; and'the chromite is substantially unattacked; and hence this range from 700 to 900 degrees is employed to eliminatethe iron and nickel as completely as possible. The residue is then carried rapidly to 1100 degrees C. or above. The fractional condensing chambers may be so arranged that the hottest vapors are slightly cooled to separate the chromium chloride, then colder vapors from an earlier stage of the heating are admitted as containing nickel and iron chlorides, and a further cooling accomplished to eliminate the nickel; and thereafter the iron chloride may-be burnt with the chlorides of silicon and aluminum, or also fractionally separated as set out above.

Example IV While the above examples are addressed to the treatment ofmixtures containing metals as such or mixtures containing reducing agents for producing the metals during the course of the chicrine treatment, it is also possible to obtain separations by treating the oxide ores, for example, directly. Thus for example a dry ore or like mixture containing iron, manganese, nickel, cobalt, chromium, aluminum, and silicon in the form of simple and complex oxides may be heated and subjected to the action.of chlorine. At 300 degrees C., substantially no change occurs. At 500 degrees C., the chromium and manganese components show gains of weight, due apparently to substitution of chlorine for oxygen in simple oxides thereof, of around 22 and 32 percent respectively, but little volatilization occurs except for loss of iron as chloride. At 700 degrees C., the nickel, chromium and manganese components continueto gain in weight, while losses of the other components occur. At 900 degrees C., about 96 percent of the iron, 72 percent of nickelous and 87 percent of nickelic oxides, 99 percent of cobalt, 33 percent of manganese, and around 5 percent of chromium, have passed over as sublimates or vapors; while the silieon and aluminum components have yet sufiered but little loss. At 1100 degrees C., the iron, cobalt, nickel, and manganese have been removed almost quantitatively,

along with around 20 percent of the chromium,

while only a few percent'of mixed silicon and aluminum chlorides have been expelled. While this method does not lend itself to selective sublimation of the chlorides, it does facilitate a quantitative and selective exclusion of certain metal values without substantial attack upon the gangue, and the evolved chlorides may be collected by fractional condensation if desired. The solid residue may be worked up for the remaining chromium. I

In general, it may be pointed out that condensation chambers maintained above 420 degrees, and to which vapors are admitted as coming from a furnace heated to 780 degrees C. or above, operate as receptors of chromium and nickel chlorides; while a chamber at 200 degrees C., which receives the issuing vapors from such a first receptor, acts to selectively collect the ferric chloride. The aluminum and silicon chloride vapors pass on through; and if further cooled, a selective separation of the aluminum chloride occurs as a substantially pure anhydrous material available for use in the 'arts.

It will be understood that "chlorine as set out above includes also the related halogens which operate similarly. or a mixture may be employed. The temperatures employed assure that both bromine and iodine are in vapor form for reactive contact.

rom the specific examples set out, the invention may obviously be employed in many ways within the scope of the appended claims.

Iclaim: Y

1. The method of separating values of chromiuin, iron and nickel from an ore containing chromite and oxide compounds of iron and nickel, the quantity of iron being predominant, in the presence of large quantities of silica and alumina as gangue, which includes the stepsof effectinga sponging reduction at substantially 1000 degrees C. of at least part of the iron and nickel, heating the absence of any quantity of reducing agent suflicient to effect reduction of the chromite, silica and alumina. whereby to provoke a driving off of iron and nickel as chlorides, fractionally condensing the vapors to separate the iron and nickel as chlorides, and again heating the residue in the presence of chlorine and a reducing agent to drive off the chromium as chromium chloride.

2. The method of separating chromium from an ore containing chromite, silica and alumina, and oxide compounds of at least one metal of the group consisting of irom and nickel, which comprises the steps of reducing at least a part of the metal compounds of said group to elemental form and chlorinating at a temperature not exceeding 1000 degrees C. in the presence of a quantity of reducing agent so limited that the metals of said group are eliminated as volatile chlorides without substantial change of the chromium. silicon, and aluminum compounds; and thereafter again reducing the residue to brin the chromium of the chromite to elemental form and then chlorinating it at a temperature not less than 1000 degrees 0. whereby to eliminate the chromium as volatile chloride without substantial change of the silica and alumina.

3. The method of recovering the values of nickel and chromium from admixture in oxide form with silica, alumina, and iron oxide compounds, which comprises efiecting a sponging reduction at substantially 1000 degrew C. for partially reducing the mixture to produce elemental nickel and iron without substantial change of chromium, silicon, and aluminum compounds, heating in the presence of chlorine at a temperature of substantially 500 degrees C. to produce an evolution of ferric chloride vapors, thereafter heating the residue in the presence of chlorine at a temperature ofsubstantially 900 degrees C. and collecting the evolved nickel chloride vapors while maintaining the quantity of reducing agent present insufiicient to cause a substantial reducing of the chromium oxide, silica and alumina matters during the latter heating, heating the solid residue in the presence of chlorine and carbon to a temperature exceeding 1000 degrees C., and collecting the vapors of nickel, iron and chromium chlorides therefrom.

of iron values, which comprises reducing at least parts of the nickel and iron in the ore by a sponging operation, treating the sponge with chlorine at an elevated temperature whereby to provoke evolution of ferric chloride vapors while substantially maintaining nickel chloride unvolatilized and the chromite unchanged, thereafter heating the sponge to provoke volatilization of nickel chloride while-leaving the chromium values substantially unchanged, and, mixing the residue with carbon and subjecting it to a further chlorine treatmentat a temperature in excess of 1000 degrees C. whereby to provoke the evolution of chromium chloride vapors. k

5. The method of separating iron, nickel and chromium values from one another and from gangue as occurring in an ore of the Cuban laterite type, which includes the steps of subjecting the ore to a low temperaturesponging in the presence of a restricted quantity of carbon whereby to reduce portions of the iron and nickel contents to elemental form, contacting the sponge with chlorine at a temperature between-400 degrees and 500 degrees C. to effect an elimination of iron as ferric chloride and a chlorinati n of the nickel, increasing the temperature to between 700 degrees and 800 degrees to effect an elimination of the nickel as nickel chloride, collecting said elim-.

inated chlorides, again reducing the residue, and subjecting it to a further chlorination to eliminate the chromium as chromium chloride.

6. The method of separating iron, nickel and chromium values from one another and from gangue as occurring in an ore of the Cuban laterite type, which includes the steps of subjecting the ore to a low temperature sponging operation for producing elemental iron and elemental nickel therefrom, heating the sponge in the presence of chlorine and substantial absence of water to a temperature of approximately 500 degrees C. to provoke an active evolution offerric chloride vapor substantially free from nickel and chromium chlorides, thereafter heating to approximately 800 degrees to effect an evolution of nickel chloride vapor substantially free from chromium chloride, mixing the residue with carbon, again subjecting it to the action of chlorine at high temperature to effect an evolution of chromium chloride while maintaining the major portion of the gangue unchanged, and fractional- -ly condensing the chromium chloride from gangue chlorides.

7. The method of separating iron, nickel and chromium values from one another and from gangue as occurring in an ore of the Cuban laterite type, which includes the steps of subjecting the ore to a low temperature sponging operation by a limited quantity of reducing agent for producing elemental iron and elemental nickel therefrom without substantial change 'of chromium values and gangue, heating the sponge.

in the presence of chlorine and substantial absence'of water and reducing agent to a temperature of approximately 500 degrees C. to provoke an active evolution of ferric chloride vapor substantially free from nickel ,and chromium chlorides, thereafter heating to approximately 800 degrees to effect an evolution of nickel chloride vapor substantially free from chromium chloride,

mixing the residue with carbon, again subjecting I it to the action of chlorine at high temperature toeifect an evolution of vapors including chromium chloride, and fractionally condensing chromium chloride from admixed vapors.

8. The method of separating iron, nickel and chromium values from one another and from gangue as occurring in an ore of the Cuban laterite type, which includes the steps of subjecting the ore to a low temperature sponging operation by a limited quantity of reducing agent i for producing elemental iron and elemental nickel therefrom, heating the sponge in the presence of chlorine and substantial absence of water and reducing agent to a temperature of approximately 500 degrees C. to provoke an active evolution of ferric chloride vapor substantially free from nickel and chromium chlorides, thereafter heating to approximately 800 degrees to effect an evolution of nickel chloride vapor substantially free from chromium chloride, mixing the residue with carbon, again subjecting it to a. secondary treatment with chlorine at high temperature to effect an-evolution of vapors including chromium chloride, and fractionally condensing the vapors from said secondary chlorine treatment to separate selectively chromium and nickel chlorides therefrom.

9. The method of separating iron, nickel and chromium values from one another and from :gangue as occurring in an ore of the Cuban laterite type, which includes the steps of subjecting the ore to a'low temperature s'ponging operation by a limited quantity of reducing agent to form elemental iron and elemental nickel therefrom, heating the sponge in the substantial absence of water vapor and reducing agent and in the presence of chlorine to a temperature of substantially 500 degrees C. to effect the elimination of iron as ferric chloride vapor, increasing the temperature in the continued presence of chlorine for a limited time to effect a partial removal of the nickel as nickel chloride vapor, again reducing the residue and subject- 'ing it to a secondary chlorine treatment at a temdegrees C. whereby to avoid reduction of chromium oxide matters subjecting the matter to a chlorine treatment in the substantial absence of water vapor and presence of a limited quantity of carbon at a temperature of substantially 500 degrees C. to expelmost of the iron therefrom as ferric chloride vapor, collecting said ferric chloride, further heating the residue to a temperature of substantially 700 degrees C. to effect an elimination of nickel as nickel chloride vapor while maintaining the quantity of carbon insufficient to cause a reduction of the chromium oxide matters and gangue, collecting the nickel chloride, and further increasing the temperature to substantially 900 degrees C. for eliminating.

the remaining iron and nickel as chloride vapors as completely as possible without conversion of the chromium and gangueto chlorine compounds.

11. The method of selectively separating iron, nickel and chromium values from oxide matters containing the same in the presence of gangue which includes the steps of chlorinating the matter in the substantial absence of water vapor and other chlorides, and fractionally condensing chromium chloridetrom the mixed vapors.

15. The method of separating chromium from an ore-containing chromite, silica and alumina, and'oxide compounds of at least one metal of the group consisting of iron and nickel, which comdegrees C. andwithdra'wing the second vapors" thus formed, increasing the temperature to at least 1100 degrees C. and withdrawing the further vapors thus formed, fractionally condensing said further vapors to separate chromium chloride therefrom, mixing the uncondensed vapors with said second vapors and further cooling to eliminate nickel chloride therefrom, and mixing the yet-uncondensed vapors with said first vapors and fractionally condensing iron chloride therefrom. T

12. The method of selectively separating iron, nickel and chromium values from matters containing the same which includes the steps of chlorinating the matter in the substantial ab-' sence of water vapor and at a temperature increasing to substantially 500 degrees C. and withdrawing the first vapors thus formed, increasing 13. The method of separating reduced iron and nickel valuesand chromium values from treated ores thereof containing chromite and containing alumina and silica as gangue, which includes the steps of heating in the presence of chlorine and absence of water vapor and substantial'absence of reducing agent to a temperature of substantially 900 degrees C. to effect an elimination of iron and nickel therefrom as volatile chlorides while the gangue and chromite remains substantially unchanged, fractionally condensing the vapors to separate nickel and iron chlorides selectively therefrom, reducing and chlorlnating the residue to decompose the chromite and effect an elimination of chromium chloride vapor therefrom. 55 14. The method of separating chromium from chromite in the presence of metals of the group consisting of iron and nickel whose chlorides have a lesser volatilizing point than chromium chloride and in the presence of alumina and silica as gangue, which includes the steps of efiecting a sponging reduction of the metals of said group at a temperature of substantially 1000 degrees C.

the temperature to approximately 900-degrees 0.

prises the steps of effecting a sponging reduction of at least a part of the metalcompounds of said group to elemental form at a temperature of substantially 1000 degrees C; whereby to avoid change of the chromite, silica and alumina and chlorinating at a temperature not exceeding 1000 degrees C. in the presence of a quantity of reducing agent so limited that the metals of said group are eliminated as volatile chlorides without sub- 15' stantial change of the chromium, silicon andaluminum compounds; andthereafter again reducing the residueto bring the chromium of the chromite to elemental form and then chlorinating it at atemperature not less than 1000 de- 20 greesC. whereby to eliminate the chromium as volatile chloride without substantial change of the silica and alumina.

16. The method of recovering thevalues of nickel and'chromium from admixture in oxide 5 form with silica,-alumina and iron oxide compounds, which comprises efiecting asponging reduction-at substantially 1000 degrees C. for partiallyreducing the mixture to produce elemental nickel and iron without substantial change of go chromium, silicon and aluminum compounds, heating in the presence of chlorine at a temperature of substantially 500 degrees C. and withdrawing the iron chloride vapors produced, thereafter heating the residue in the presence of chlo- 35 rine at a temperature of substantially 800 degrees and for a limited time to effect a partial elimination of the nickel as nickel chloride while retaining a portion of the nickel in the residue, remov- -ing the evolved nickel chloride; and thereafter treating the residue with a reducing agent and with chlorine at high temperatures to drive out whereby to leave the chromite, alumina and silica substantially unchanged, subjecting the sponged 5 matter to a chlorine treatment under anhydrous conditions and in the absence of any substantial quantity of reducing agent at an elevated temperature suificient to effect an elimination of the reduced metals of said group from said sponged matter as volatile chlorides and insufiicient with the limited quantity of reducing agent to efiect a substantial chlorination of the chromite and gangue, reducing the residue and again chlorinating to cause a volatilization of the chromium 7 as chromium chloride in mixture with vapors of the remaining nickel and chromium as chlorides.

17. The method of separating chromium, nickel and iron values from ores or the laterite type 45 containing silica and alumina as gangue, which comprises mixing the calcined ore with carbon and heating under anhydrous conditions and in the presence of chlorine to a temperature of substantially 500 degrees C. and withdrawing the 50 iron chloride vapors produced, heating in the continued presence of chlorine to 'a temperature of substantially 700 degrees C. and withdrawing the second vapors thus produced, fractionally condensing nickel chloride from these second vapors and mixing the uncondensed vapors with said iron chloride vapors, heating in the continued presence of chlorine and to a temperature of substantially 900 degrees C. and for a time to effect a substantially complete elimination of iron and nickel from the residue in the substantial absence of a reducing agent so that silica and alumina are substantially unattacked, and withdrawing the vapors formed, and then rapidly heating the residue to substantially 1100 degrees C. in the presence of chlorine for effecting the elimination of chromium as'chromium chloride, withdrawing the vapors thus formed and fractionally condensing chromium chloride therefrom.

18. The method of separating chromium, nick- 7Q el and iron values from ores of the laterite type containing large quantities of silica and alumina and silica are substantially unchanged, heating the sponge under anhydrous conditions in the presence of chlorine to a temperature of substantially 500 degrees C. and withdrawing the iron chloride vapors produced, thereafter heating the residue to a temperature of 800 to 900 degrees C. and withdrawing and separating by fractionalstantially complete elimination of iron, nickel and chromium as volatile chlorides.'

19. The method of recovering the values of iron, nickel and chromium from ores of the laterite: type containing alumina and silica as gangue, which comprises eflecting a sponging reduction at substantially 1000 degrees C. so' that 2,oso,ses

the silica and alumina are substantially unchanged, treating withchlorine under anhydrous conditions at a temperature of substantially 500 degrees and withdrawing the iron chloride vapors produced, heating the residue at a temperature of substantially 800 degrees C. in the substantial absence or a reducing agent so that the silica and alumina remain substantially unchanged and' withdrawing the mixed vapors of iron, nickel and chromium chlorides produced, burning the said vapors to produce the corresponding oxides and returning the chlorine in cycle,'and heating the remaining residue in the presence of a reducing agent for reducing the chromium oxide compounds present and in the presence ot ch'lorine' tor eflecting an elimination ot the elemental chromium as volatile chloride.

CHARLES HART. 

